To meet the demand for higher integration density and operating speed of LSIs, the effort to reduce the pattern rule is in rapid progress. The wide-spreading flash memory market and the demand for increased storage capacities drive forward the miniaturization technology. As the advanced miniaturization technology, manufacturing of microelectronic devices at the 65-nm node by the ArF lithography has been implemented in a mass scale. Manufacturing of 45-nm node devices by the next generation ArF immersion lithography is approaching to the verge of high-volume application. The candidates for the next generation 32-nm node include ultra-high NA lens immersion lithography using a liquid having a higher refractive index than water in combination with a high refractive index lens and a high refractive index resist film, extreme ultraviolet (EUV) lithography of 13.5 nm wavelength, and double patterning version of the ArF lithography, on which active research efforts have been made.
With respect to high-energy radiation of very short wavelength such as electron beam (EB) or x-ray, hydrocarbons and similar light elements used in resist materials have little absorption. Then polyhydroxystyrene base resist materials are under consideration. Resist materials for EB lithography are practically used in the mask image writing application.
Recently, the mask manufacturing technology becomes of greater interest. Reduction projection exposure systems or steppers have been used since the time when the exposure light was g-line. While their demagnification factor was ⅕, a factor of ¼ is now used as a result of chip size enlargement and projection lens diameter increase. It becomes of concern that a dimensional error of a mask has an impact on the dimensional variation of a pattern on wafer. It is pointed out that as the pattern feature is reduced, the value of a dimensional variation on the wafer becomes greater than the value of a dimensional error of the mask. This is evaluated by a mask error enhancement factor (MEEF) which is a dimensional variation on wafer divided by a dimensional error of mask. Patterns on the order of 45 nm often show an MEEF in excess of 4. In a situation including a demagnification factor of ¼ and a MEEF of 4, the mask manufacture needs an accuracy substantially equivalent to that for equi-magnification masks.
The exposure system for mask manufacturing made a transition from the laser beam exposure system to the EB exposure system to increase the accuracy of line width. Since a further size reduction becomes possible by increasing the accelerating voltage of the electron gun in the EB exposure system, the accelerating voltage increased from 10 keV to 30 keV and reached 50 keV in the current mainstream system, with a voltage of 100 keV being under investigation.
In a chemically amplified resist composition comprising an acid generator which generates an acid upon exposure to light or EB to induce deprotection reaction, a quencher is often added for the purpose of controlling diffusion of the acid into the unexposed area for improving the contrast. Since the addition of such quenchers is quite effective, numerous amine quenchers have been proposed. As pointed out in the art, the amine quenchers give rise to a problem that the profile and size of a pattern vary due to evaporation and re-deposition of acid and amine quencher during bake. This phenomenon may occur on use of either a dark mask in which a peripheral portion of a line-and-space pattern is light shielded or a bright mask in which the peripheral portion is transparent. Since no light is irradiated in the peripheral portion of the dark mask, the amine quencher is in excess in the resist film. In the peripheral portion of the bright mask, the acid generated by light irradiation is in excess. While the deformation of pattern by evaporation and re-deposition of acid has been mainly discussed, evaporation of amine quencher is also troublesome.
As the acid generator, alkylsulfonium salts such as 4-alkoxy-1-naphthyltetrahydrothiophenium cations were developed. These alkylsulfonium salts are susceptible to nucleophilic displacement reaction by amines or the like so that the resist solution may increase its sensitivity. Their low stability is a problem. It would be desirable to have an amine quencher which does not induce nucleophilic displacement reaction to these acid generators. Although those amine quenchers of weak bases such as pyridine and aniline do not induce nucleophilic displacement reaction, undesirably they have low acid trapping and acid diffusion controlling capabilities.
While the EUV and EB lithography processes involve exposure in vacuum, a sensitivity increase due to evaporation of the quencher during exposure is pointed out. Also image blur by diffusion of amine quencher is pointed out. It would be desirable to have a quencher which does not adversely affect the stability of a resist composition, does not substantially evaporate or diffuse by heat, and has a good acid trapping capability.
Heretofore, resist resins in the form of polymers having amine incorporated in polymer units have been proposed for the purposes of reducing leach-out of basic components during exposure by immersion lithography and improving lithography properties such as depth of focus (DOF) (see JP-A 2008-133312 and JP-A 2009-181062). These resins are effective for controlling volatilization and diffusion of quenchers, but are still insufficient in roughness reduction or the like.
Also a variety of carbamate quenchers such as tert-butoxycarbonyl amine have been developed for the purposes of improving the margin of an isolated pattern and improving the stability of resist composition (see JP 3790649 and JP-A 2007-298569). These carbamate quenchers are low basic and effective for improving the stability of the foregoing acid generators, but are still unsatisfactory with respect to the control of volatilization and diffusion of the quencher.